Conventionally, there has been provided a load control system for operating only a preset load by supplying a power from a backup power supply to the corresponding load during a power failure (see, e.g., Japanese Patent Laid-open Publication No. 2009-148009).
The load control system described in Patent Document 1 supplies a DC power from a main power supply to DC devices connected to DC power supply lines and also supplies a backup power from a backup power supply provided in addition to the main power supply to the DC devices via the DC power supply lines during a power failure in the main power supply. Thus, the DC devices can operate for a predetermined period of time even during the power failure in the main power supply.
In the above-described load control system, when the power is supplied from the backup power supply to all the DC devices connected to the DC power supply lines during the power failure, the backup power supply is used intensively. Therefore, the power is backed up only for a short period of time, which results in requirement of a large capacity backup power supply. Hence, in the load control system described in Patent Document 1, the DC devices are configured to have communications functions, and operation stop is instructed to the DC devices having low priority through communications when a power failure occurs. As a consequence, the power consumption is reduced, and the power backup time is extended.
In such load control system, since the load devices need to have the communications functions for instructing the operation stop during the power failure, the cost of the system increases and specific load devices having the communications functions are required.